1. Once you reach a goal you've set for yourself, the moment of celebration that comes with achieving it is fleeting. You want more, and now that you've reached that specific goal, you're immediately onto other ones. Most times, starting again from scratch. This sort of blunts the impact of achieving said goal.

2. Goals are worthless without action. Here's a quote from Earl Nightengale's "The Strangest Secret":

“We’ve got to put the fuel in before we can expect heat. Likewise, we’ve got to be of service first before we can expect money. Don’t concern yourself with the money. Be of service. Build. Work. Dream. Create. Do this and you’ll find that there is no limit to the prosperity and abundance that will come to you.”

3. In order to achieve a goal, you'll likely need to set dozens of other smaller goals in order to achieve the bigger goal. Hitting those small goals are nice but, see #1.

Arthur Ashe once said, "Success is a journey, not a destination. The doing is often more important than the outcome." I find this to be half true. Do you think all of Michael Jordan's hard work would have been just as meaningful if he didn't win any championships? I don't think so. After he won his first championship, I'm sure he was ecstatic about his achievement. But it's not enough. He wanted more. And more. And more.